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Abstract

Optimization of process parameters is the key step in response surface methods to achieve high quality without cost inflation. The multi-response optimization of the machining parameters viz, chip-tool interface temperature, main cutting force and feed force on lathe turning of En-31 steel as alloy steel using RSM with grey relational analysis is reported. A grey relational grade obtained from the grey relational analysis is used to solve the turning operations with multiple performance characteristics. The models were developed using response surface methodology. Optimal cutting parameters can be determined by RSM method using the grey relational grade as the performance index. Chip-tool interface temperature, main cutting force, and feed force are important characteristics in turning operations. Using these characteristics, the cutting operations, including cutting velocity, feed rate, depth of cut, and effective tool nose radius, are optimized. A model is developed to correlate the multiple performance characteristic called grey relational grade and turning parameters and a new combination of RSM and grey relational analysis is proposed. The grey relational grades were significantly affected by cutting parameters and tool nose radius. Optimal parameter setting is determined for the multi-performance characteristic.

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1. Introduction

Turning operations are widely used in workshop practice for applications carried out in conventional machine tools, as well as in NC and CNC machine tools, machining centers and related manufacturing systems. Turning machining involves the use of a lathe and is used primarily to produce conical cylindrical parts. With common attachments, flat faces, curved surfaces, grinding and boring can be done with a lathe. Therefore, it is valuable to increase tool life, to improve surface accuracy, to reduce main cutting force, feed force and to reduce machining zone temperatures (chip-tool interface temperature) in turning operations through an optimization study.

In turning operation the resultant force is divided into three force components, main cutting force, feed force and radial force. All three force components are of interest because apart from the main component that gives the cutting power and its determination is apparently necessary, the radial and feed components control dimensional and form errors in case of workpiece and tool deflection and tool wear. Usually, in metal cutting operation the main cutting force is the largest force as compared to feed force and radial force (Trent, 1991). One of the most important phenomenons occurring during the machining process is that heat generation in the machining zone. Researchers, Shaw (2004) and Komanduri (2001) agree that most of the energy applied to the cutting process is converted into heat in the machining zone of plastic deformation, the shearing plane, where the workpiece material turns itself in to chip and in the secondary zone of plastic deformation, where chip slides on the rake face. Finally, some heat also arises on the tertiary zone, where the tool relief face slides on the newly machined surface. This last source is, however, not considered in most cases, either for simplicity, or because the heat generated is very small when using sharp cutting edges. The heat generated in those machining zones is distributed among the cutting tool, the workpiece, the chip, and after that to the environment. Heat generated at the machining zone (shearing plane) can make the metal cutting action easy, but it can flow into the cutting edge and that will negatively affect the tool life by shortening it. When machining steel with cutting tools different tool wear mechanism occur, such as, abrasion, adhesion, oxidation, and even some diffusion, which act simultaneously and in proportions depending mainly on the cutting temperature. However, some researchers relating wear mechanisms to the cutting speed have been made and some important results have been published. For example the raise in cutting temperature at the machining zone occurs basically due to the cutting speed increase. Author (2010) reported, the cutting speed is main influencing factor on chip-tool interface temperature as compared to others. It has been shown that increasing cutting speed, feed rate and depth of cut lead to an increase in cutting temperature. However, increasing the tool nose radius decreases the cutting temperature.